The present invention relates to the medical diagnostic and surgical arts and is particularly related to a surgical tool support apparatus that is (i) MR-Safe and MR-compatible and/or (ii) X-Ray/CT compatible for use in the operative environment of an imaging modality. The present invention finds particular application in conjunction with neurosurgery and will be described with particular respect thereto. It will be appreciated, however, that the invention finds application in conjunction with biopsies, endoscopic procedures, orthopedic surgeries, other medical procedures, industrial quality control procedures, and the like in which a tool or device must be accurately positioned in relation to an object.
Image guided surgery systems are particularly well adapted to intra-cranial and spinal surgery. These systems use diagnostic images of the patient to assist the physician with presurgical planning and to provide information relating to the position and orientation of the anatomy and instrumentation during a surgical procedure. Image guided surgery systems are well-suited for use in connection with magnetic resonance ("MR") and computerized tomography ("CT") images, as well as with other imaging modalities. well-suited for use in connection with magnetic resonance ("MR") and computerized tomography ("CT") images, as well as with other imaging modalities.
In cranial applications, a patient reference frame may be defined using three or more points fixed in relation to the patient's head. According to one method, at least three markers visible to the imaging device are affixed to the skin prior to imaging. According to another method, anatomical reference points are used. According to a third method, fiducial markers may be affixed to the skull, for example as disclosed in U.S. Pat. No. 4,991,579, Method and Apparatus for Providing Related Images of the Anatomy over time of a Portion of the Anatomy Using Fiducial Implants, to Allen, issued Feb. 12, 1991. Similar techniques may be used to define a patient reference frame with respect to other portions of the anatomy.
An image of the patient having an image reference frame is then obtained. Based on the location of the three or more markers within the image data, the image and patient reference frames can be correlated. Hence, the position of a feature of interest within the image can be determined with respect to the patient reference frame. After image acquisition is complete, the patient can be moved as desired. The patient is subsequently placed in an operating room environment, for example on an operating table.
The patient and operating room reference frames are correlated or "zeroed" by touching the surgical tool to the at least three markers. The position of the tool with respect to the cameras, and hence the position of the markers, is then determined. Inasmuch as the relationship between the patient, operating room, and image frames of reference is known, the position of the tool with respect to the image reference frame can then be determined. Relevant images, with the position of the surgical tool indicated thereon, are then displayed on a monitor. The surgeon is thus provided with a real time indication of the position of the surgical tool with respect to the previously obtained image.
In order to assist in the accurate positioning of surgical tools, neurosurgical procedures such as brain biopsies can be performed using a positioning apparatus such as a surgical guide. The surgeon uses the image guided surgery system to assist in positioning and orienting the guide. The guide is used to guide a biopsy needle or other surgical instrument along the desired trajectory.
Greenberg and Bookwalter clamps marketed by Johnson and Johnson Professional, Inc, a subsidiary of Johnson and Johnson, as part of their Codman line of surgical instruments, have been used as positioning devices for surgical procedures. These devices consist of a series of links that are held in compression by a cable going through the centers of the links, forming a pre-loaded gooseneck mechanism. A clamping mechanism at the lower end of the devices attaches to the operating table or to the patient restraint apparatus. A clamping mechanism at the upper end of the devices holds the surgical instrument. Several reducing tubes of different sizes are used to adapt the devices to hold different instruments. Designs of gooseneck-type surgical positioning devices are described in U.S. Pat. Nos. 4,573,452 by Greenberg, 5,662,300 by Michelson. Use of a ball joint in a surgical positioning device is described in U.S. Pat. No. 5,320,444 by Bookwalter.
It is becoming increasingly desirable to perform MR-guided or MR-assisted interventional surgical procedures, which are ordinarily conducted in the immediate vicinity of a magnetic resonance imaging scanner. These procedures require, however, that the equipment used be MR-safe, meaning that it will not be adversely affected by the magnetic and electric fields of the scanner. Furthermore, to perform such procedures inside the imaging volume of an MRI scanner without degradation of the scanner's imaging performance, the devices must be MR-compatible, meaning that they do not disturb the magnetic or electric fields of the scanner, and do not emit MR signals with the imaging sequences being used. For other imaging modalities, such as X-Ray, CT or Fluoroscopic imaging systems, the term compatible indicates that the device is generally transparent in an image when the device is placed in the operating environment of those imaging modalities.
The Greenberg and Bookwalter clamps described above are fabricated from stainless steel. Therefore, they are not MR-compatible as they disturb the homogeneity of the magnetic and electric fields. At the edges of the magnetic field, these devices may experience magnetic forces and thus are not MR-safe. The introduction of an electrically conductive device can introduce eddy currents which deleteriously affect the magnetic fields within the MR scanner. Yet another disadvantage to the introduction of an electrically conductive device is that the likelihood of inadvertent connections or short circuits between electrical devices in the area is increased. As a result, the Greenberg and Bookwalter clamps are not suitable for use in MR-guided or MR-assisted surgical procedures.
As an alternative to stainless steel, positioning devices have been fabricated from titanium. For example, Bookwalter clamps for interventional MR use have also been fabricated from titanium. While devices fabricated from titanium are not affected by the magnetic fields of the MR scanner and are therefore MR-safe, they are not MR-compatible. Titanium devices also do not address the issues noted above in regard to electrical conductivity. Another disadvantage of devices fabricated from titanium is their high cost.
Hence, a surgical guide which is both MR-safe and MR-compatible is needed. It is also desirable to perform interventional surgical procedures in the operative environment of other imaging modalities such as X-Ray and CT and Fluoroscopic imaging systems. A compatible device in these environments should be unaffected by and substantially transparent to the imaging system. Such devices should allow the trajectory of the surgical tool be readily adjusted while providing stable and accurate guidance. The guide should also be unobtrusive, easy to use, and usable with a variety of surgical tools.